The proposed research is a combined genetic and biochemical study of mitochondrial (mt) biogenesis in Neurospora with the long range goals of defining the roles of the nuclear and mitochondrial genetic systems and understanding how these roles are coordinated and modulated. We propose to continue biochemical and genetic analysis of mt ribosome assembly in wild type and in mutants with defects in mt ribosome assembly. In previous work, we identified one mt ribosomal protein (S-5, Mr 52,000) which is synthesized within the mitochondria. In the proposed research, we would continue to study the role of this protein in mt ribosome assembly and mt protein synthesis by direct biochemical approaches such as partial in vitro reconstitution. We would also continue to examine the relationship of S-5 to the etiology of (poky) and other Group I extra-nuclear mutants with defects in mt ribosome assembly. In another approach, we have recently identified deletion mutants of Neurospora mtDNA. In the proposed research, we would continue to study such mutants and attempt to use them to map Neurospora mtDNA, focusing first on genes involved in mt ribosome assembly.